Processes for preparing propylene oxide employing alkylaryl hydroperoxide compounds, are well known in the art. As described in U.S. Pat. No. 5,883,268, such processes conventionally comprise peroxidation of ethylbenzene, followed by contacting the peroxidation reaction product with aqueous base in amount sufficient to neutralize acidic components thereof and separating the resulting mixture into an aqueous stream and a deacidified organic stream. The base contaminated, deacidified hydroperoxide stream is washed with water and the resulting mixture separated into an organics contaminated water phase and an organic phase having a reduced alkali metal content.
It has now been found that the peroxidation reaction product does not need to be washed with aqueous base. Surprisingly, the peroxidation reaction product can be washed with water only. An important advantage of the absence of a wash with aqueous base is that a larger amount of aqueous phase is allowable in the organic phase. The larger amount of aqueous phase is acceptable in the process according to the present invention as such aqueous phase will not contain aqueous base residue such as sodium salts. The presence of such compounds generally causes the problems in subsequent process steps. Water does not need to be rigorously removed in the process of the present invention and this makes that the separation of water and organic phase can be carried out in a more simple way. Furthermore, upsets in the plant leading to less efficient water removal are more acceptable in the present invention than they are in a conventional process.
It was found that alkylaryl hydroperoxide containing reaction product which was washed with water only, gave similar catalyst deactivation in a subsequent reaction as product washed with both aqueous base and water, while a higher yield of alkylaryl hydrogen peroxide was observed when the reaction product had been washed with water only. The latter is attributed to reduced decomposition of alkylaryl hydrogen peroxide. Such decomposition is thought to be catalysed by the presence of aqueous base at basic conditions. The similar deactivation is very surprising as a water wash removes very little contaminants such as benzoic acid, which are known to be present in the crude reaction product. Furthermore, less emulsion was observed to be formed when the alkylaryl hydroperoxide containing product was washed with water only.
WO 00/12470 describes a process for purifying a cyclohexyl hydroperoxide containing reaction mixture in order to make it suitable for decomposition or hydrogenation into cyclohexanol and cyclohexanone. This document contains no information on purification of an akylaryl hydroperoxide containing reaction mixture to be reacted with olefin in the presence of an epoxidation catalyst.